There is known a hybrid vehicle including a power source such as an electromotor and a motor generator, in addition to an engine. In the hybrid vehicle, while the engine operates as efficiently as possible, excess and deficiency of a driving force and an engine braking force are adjusted by the electromotor and/or the motor generator.
As for the above hybrid vehicle, there is disclosed an example of a speed change mechanism capable of operating with switching an infinite variable speed mode and a fixed gear ratio mode in Patent Reference 1. Concretely, a power distribution mechanism including four revolution components is formed by combining two planetary gear mechanisms, and the four revolution components are connected to an engine, a first motor generator, an output axis and a brake, respectively. In such a state that the brake is released, the number of revolutions of the engine continuously changes by continuously changing the number of revolutions of the first motor generator, and the operation in the infinite variable speed mode is executed. Meanwhile, in such a state that the brake is fixed, the gear ratio is fixed by preventing the revolution of one of the above-mentioned revolution components, and the operation in the fixed gear ratio mode is executed. In addition, as the speed change mechanism for switching the infinite variable speed mode and the fixed gear ratio mode, there is known a speed change mechanism which applies not a normal wet multiple disc clutch but an engagement mechanism for engaging teeth of the revolution component and teeth of the fixed component.
[Patent Reference 1] Japanese Patent Application Laid-open under No. 2004-345527
In the technique disclosed in Patent Reference 1, drivability sometimes deteriorates because the number of engine revolutions changes at the time of shifting the speed gear between the infinite variable speed mode and the fixed gear ratio mode. For example, when the speed gear is shifted from the fixed gear ratio mode to the infinite variable speed mode and acceleration is executed, the number of engine revolutions decreases once, and uncomfortable feeling sometimes occurs.